What percentage of patients taking Proscar (finasteride) experience erectile dysfunction?

Erectile Dysfunction Rates with Proscar (Finasteride)

Proscar (finasteride 5 mg) causes erectile dysfunction in approximately 2-4% more patients compared to placebo, with the highest incidence occurring during the first year of treatment.

Incidence Data from Clinical Trials

First Year of Treatment

The most robust data comes from large-scale randomized controlled trials showing:

• 8.1% of finasteride-treated patients experienced impotence/erectile dysfunction versus 3.7% on placebo in Year 1 1, 2
• This represents an absolute increase of approximately 4.4% attributable to the drug 1
• When examining all mid-term studies (1-2 years), the relative risk ranged from 0.90 to 11.33, with most studies showing a 2-4% absolute increase 1

Long-Term Treatment (Years 2-4)

Importantly, the sexual dysfunction associated with finasteride decreases substantially over time 1:

• In Years 2-4, the incidence of impotence was 5.1% in both finasteride and placebo groups (no significant difference) 1, 2
• New sexual adverse events occurred in only 7% of both finasteride and placebo patients during years 2-4 3
• The sexual dysfunction that occurs in Year 1 often resolves while continuing therapy in 12% of finasteride patients 3

Context and Clinical Significance

Magnitude of Effect

The sexual dysfunction effect is relatively modest when placed in proper context 1:

• On a 0-100 scale measuring sexual dysfunction, finasteride caused a mean difference of 3.21 points compared to placebo 1
• For comparison, each year of aging causes a mean difference of 1.26 points 1
• This suggests the drug effect is approximately 2.5 times the annual effect of natural aging 1

Discontinuation Rates

Only 3.7% of finasteride patients discontinued due to sexual adverse effects (versus 2.1% on placebo) 2:

• The combined discontinuation rate for all adverse events was approximately 6% in both finasteride and placebo groups 1
• Among those who discontinued due to sexual adverse effects, 50% experienced resolution after stopping finasteride 3

Important Caveats

Nocebo Effect

The reported incidence of sexual dysfunction may be significantly influenced by patient counseling 4:

• When patients were informed about potential sexual side effects, the incidence was 43.6% 4
• When the same information was omitted, the incidence was only 15.3% 4
• This suggests a substantial nocebo component to reported sexual dysfunction 4

Baseline Sexual Dysfunction

46% of men in clinical trials had pre-existing sexual dysfunction at baseline 1, 2, making attribution to finasteride challenging in some cases.

Persistent Dysfunction

While most sexual adverse effects resolve, rare cases of persistent erectile dysfunction (lasting >90 days after discontinuation) have been reported, though the exact incidence remains uncertain 5.

Practical Recommendations

Counsel patients that:

• Sexual side effects occur in approximately 2-4% more patients than placebo 1
• These effects are most common in the first year and often diminish with continued treatment 1, 3
• The effects are usually reversible upon discontinuation 1
• The magnitude is relatively small compared to natural aging 1